Method for acquiring synchronization in a communication system and device therefor

ABSTRACT

The present invention relates to a wireless communication system. More specifically, the present invention relates to a method for acquiring, by a first user equipment (UE) in a coverage of a first cell, synchronization in a wireless communication system, the method comprising: receiving a message for a sidelink resource configuration from a second cell through the second UE in a coverage of the second cell; if a channel quality of the second cell is less than a predetermined threshold, selecting the first cell as a synchronization reference cell; and transmitting a sidelink data to the second UE using the sidelink resource configuration based on the synchronization acquired from a synchronization signal of the first cell.

This application claims the benefit of the U.S. Provisional Patent Application No. 62/367,079 filed on Jul. 26, 2016, which is hereby incorporated by reference as if fully set forth herein.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a wireless communication system and, more particularly, to a method for acquiring synchronization in a communication system and a device therefor.

Discussion of the Related Art

As an example of a mobile communication system to which the present invention is applicable, a 3rd Generation Partnership Project Long Term Evolution (hereinafter, referred to as LTE) communication system is described in brief.

FIG. 1 is a view schematically illustrating a network structure of an E-UMTS as an exemplary radio communication system. An Evolved Universal Mobile Telecommunications System (E-UMTS) is an advanced version of a conventional Universal Mobile Telecommunications System (UMTS) and basic standardization thereof is currently underway in the 3GPP. E-UMTS may be generally referred to as a Long Term Evolution (LTE) system. For details of the technical specifications of the UMTS and E-UMTS, reference can be made to Release 7 and Release 8 of “3rd Generation Partnership Project; Technical Specification Group Radio Access Network”.

Referring to FIG. 1, the E-UMTS includes a User Equipment (UE), eNode Bs (eNBs), and an Access Gateway (AG) which is located at an end of the network (E-UTRAN) and connected to an external network. The eNBs may simultaneously transmit multiple data streams for a broadcast service, a multicast service, and/or a unicast service.

One or more cells may exist per eNB. The cell is set to operate in one of bandwidths such as 1.25, 2.5, 5, 10, 15, and 20 MHz and provides a downlink (DL) or uplink (UL) transmission service to a plurality of UEs in the bandwidth. Different cells may be set to provide different bandwidths. The eNB controls data transmission or reception to and from a plurality of UEs. The eNB transmits DL scheduling information of DL data to a corresponding UE so as to inform the UE of a time/frequency domain in which the DL data is supposed to be transmitted, coding, a data size, and hybrid automatic repeat and request (HARQ)-related information. In addition, the eNB transmits UL scheduling information of UL data to a corresponding UE so as to inform the UE of a time/frequency domain which may be used by the UE, coding, a data size, and HARQ-related information. An interface for transmitting user traffic or control traffic may be used between eNBs. A core network (CN) may include the AG and a network node or the like for user registration of UEs. The AG manages the mobility of a UE on a tracking area (TA) basis. One TA includes a plurality of cells.

Although wireless communication technology has been developed to LTE based on wideband code division multiple access (WCDMA), the demands and expectations of users and service providers are on the rise. In addition, considering other radio access technologies under development, new technological evolution is required to secure high competitiveness in the future. Decrease in cost per bit, increase in service availability, flexible use of frequency bands, a simplified structure, an open interface, appropriate power consumption of UEs, and the like are required.

SUMMARY OF THE INVENTION

The object of the present invention can be achieved by providing a method for acquiring, by a first user equipment (UE) in a coverage of a first cell, synchronization in a wireless communication system, the method comprising: receiving a message for a sidelink resource configuration from a second cell through the second UE in a coverage of the second cell; if a channel quality of the second cell is less than a predetermined threshold, selecting the first cell as a synchronization reference cell; and transmitting a sidelink data to the second UE using the sidelink resource configuration based on the synchronization acquired from a synchronization signal of the first cell.

In another aspect of the present invention provided herein is first user equipment (UE) in a coverage of a first cell in a wireless communication system, the first UE comprising: a transceiver; and a processor connected with the transceiver, wherein the processor is configured to: control the transceiver to receive a message for a sidelink resource configuration from a second cell through the second UE in a coverage of the second cell, if a channel quality of the second cell is less than a predetermined threshold, select the first cell as a synchronization reference cell, and control the transceiver to transmit a sidelink data to the second UE using the sidelink resource configuration based on the synchronization acquired from a synchronization signal of the first cell.

Preferably, if the channel quality of the second cell is higher than or equal to the predetermined threshold, the second cell is selected as the synchronization reference cell.

Preferably, the method further comprises measuring a channel quality of the second cell and one or more neighboring cells of the first UE.

Preferably, if the channel quality of the second cell is less than the predetermined threshold, the first UE selects one of the one or more neighboring cells as the synchronization reference cell based on the channel quality.

Preferably, the method further comprises acquiring the synchronization from the synchronization signal of the first cell.

Preferably, the predetermined threshold is received from the second cell.

Preferably, the first UE is connected to the second cell through the second UE.

It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention.

FIG. 1 is a diagram showing a network structure of an Evolved Universal Mobile Telecommunications System (E-UMTS) as an example of a wireless communication system;

FIG. 2A is a block diagram illustrating network structure of an evolved universal mobile telecommunication system (E-UMTS), and FIG. 2B is a block diagram depicting architecture of a typical E-UTRAN and a typical EPC;

FIG. 3 is a diagram showing a control plane and a user plane of a radio interface protocol between a UE and an E-UTRAN based on a 3rd generation partnership project (3GPP) radio access network standard;

FIG. 4 is a diagram of an example physical channel structure used in an E-UMTS system;

FIG. 5 is a diagram for a general overview of the LTE protocol architecture for the downlink;

FIG. 6 is an example of default data path for a normal communication;

FIGS. 7 and 8 are examples of data path scenarios for a proximity communication;

FIG. 9 is a conceptual diagram illustrating for a non-roaming reference architecture;

FIG. 10 is a conceptual diagram illustrating for a Layer 2 Structure for Sidelink;

FIG. 11 a is a conceptual diagram illustrating for User-Plane protocol stack for ProSe Direct Communication, and FIG. 11b is Control-Plane protocol stack for ProSe Direct Communication;

FIG. 12 is a conceptual diagram illustrating for a PC5 interface for ProSe Direct Discovery;

FIG. 13 is an exemplary diagram for explaining the D2D environment;

FIG. 14 is a flow chart according to an embodiment of the present invention;

FIG. 15 is a flowchart for explaining an embodiment of the present invention;

FIG. 16 is a block diagram of a communication apparatus according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Universal mobile telecommunications system (UMTS) is a 3rd Generation (3G) asynchronous mobile communication system operating in wideband code division multiple access (WCDMA) based on European systems, global system for mobile communications (GSM) and general packet radio services (GPRS). The long-term evolution (LTE) of UMTS is under discussion by the 3rd generation partnership project (3GPP) that standardized UMTS.

The 3GPP LTE is a technology for enabling high-speed packet communications. Many schemes have been proposed for the LTE objective including those that aim to reduce user and provider costs, improve service quality, and expand and improve coverage and system capacity. The 3G LTE requires reduced cost per bit, increased service availability, flexible use of a frequency band, a simple structure, an open interface, and adequate power consumption of a terminal as an upper-level requirement.

Hereinafter, structures, operations, and other features of the present invention will be readily understood from the embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Embodiments described later are examples in which technical features of the present invention are applied to a 3GPP system.

Although the embodiments of the present invention are described using a long term evolution (LTE) system and a LTE-advanced (LTE-A) system in the present specification, they are purely exemplary. Therefore, the embodiments of the present invention are applicable to any other communication system corresponding to the above definition. In addition, although the embodiments of the present invention are described based on a frequency division duplex (FDD) scheme in the present specification, the embodiments of the present invention may be easily modified and applied to a half-duplex FDD (H-FDD) scheme or a time division duplex (TDD) scheme.

FIG. 2A is a block diagram illustrating network structure of an evolved universal mobile telecommunication system (E-UMTS). The E-UMTS may be also referred to as an LTE system. The communication network is widely deployed to provide a variety of communication services such as voice (VoIP) through IMS and packet data.

As illustrated in FIG. 2A, the E-UMTS network includes an evolved UMTS terrestrial radio access network (E-UTRAN), an Evolved Packet Core (EPC) and one or more user equipment. The E-UTRAN may include one or more evolved NodeB (eNodeB) 20, and a plurality of user equipment (UE) 10 may be located in one cell. One or more E-UTRAN mobility management entity (MME)/system architecture evolution (SAE) gateways 30 may be positioned at the end of the network and connected to an external network.

As used herein, “downlink” refers to communication from eNodeB 20 to UE 10, and “uplink” refers to communication from the UE to an eNodeB. UE 10 refers to communication equipment carried by a user and may be also referred to as a mobile station (MS), a user terminal (UT), a subscriber station (SS) or a wireless device.

FIG. 2B is a block diagram depicting architecture of a typical E-UTRAN and a typical EPC.

As illustrated in FIG. 2B, an eNodeB 20 provides end points of a user plane and a control plane to the UE 10. MME/SAE gateway 30 provides an end point of a session and mobility management function for UE 10. The eNodeB and MME/SAE gateway may be connected via an Si interface.

The eNodeB 20 is generally a fixed station that communicates with a UE 10, and may also be referred to as a base station (BS) or an access point. One eNodeB 20 may be deployed per cell. An interface for transmitting user traffic or control traffic may be used between eNodeBs 20.

The MME provides various functions including NAS signaling to eNodeBs 20, NAS signaling security, AS Security control, Inter CN node signaling for mobility between 3GPP access networks, Idle mode UE Reachability (including control and execution of paging retransmission), Tracking Area list management (for UE in idle and active mode), PDN GW and Serving GW selection, MME selection for handovers with MME change, SGSN selection for handovers to 2G or 3G 3GPP access networks, Roaming, Authentication, Bearer management functions including dedicated bearer establishment, Support for PWS (which includes ETWS and CMAS) message transmission. The SAE gateway host provides assorted functions including Per-user based packet filtering (by e.g. deep packet inspection), Lawful Interception, UE IP address allocation, Transport level packet marking in the downlink, UL and DL service level charging, gating and rate enforcement, DL rate enforcement based on APN-AMBR. For clarity MME/SAE gateway 30 will be referred to herein simply as a “gateway,” but it is understood that this entity includes both an MME and an SAE gateway.

A plurality of nodes may be connected between eNodeB 20 and gateway 30 via the S1 interface. The eNodeBs 20 may be connected to each other via an X2 interface and neighboring eNodeBs may have a meshed network structure that has the X2 interface.

As illustrated, eNodeB 20 may perform functions of selection for gateway 30, routing toward the gateway during a Radio Resource Control (RRC) activation, scheduling and transmitting of paging messages, scheduling and transmitting of Broadcast Channel (BCCH) information, dynamic allocation of resources to UEs 10 in both uplink and downlink, configuration and provisioning of eNodeB measurements, radio bearer control, radio admission control (RAC), and connection mobility control in LTE_ACTIVE state. In the EPC, and as noted above, gateway 30 may perform functions of paging origination, LTE-IDLE state management, ciphering of the user plane, System Architecture Evolution (SAE) bearer control, and ciphering and integrity protection of Non-Access Stratum (NAS) signaling.

The EPC includes a mobility management entity (MME), a serving-gateway (S-GW), and a packet data network-gateway (PDN-GW). The MME has information about connections and capabilities of UEs, mainly for use in managing the mobility of the UEs. The S-GW is a gateway having the E-UTRAN as an end point, and the PDN-GW is a gateway having a packet data network (PDN) as an end point.

FIG. 3 is a diagram showing a control plane and a user plane of a radio interface protocol between a UE and an E-UTRAN based on a 3GPP radio access network standard. The control plane refers to a path used for transmitting control messages used for managing a call between the UE and the E-UTRAN. The user plane refers to a path used for transmitting data generated in an application layer, e.g., voice data or Internet packet data.

A physical (PHY) layer of a first layer provides an information transfer service to a higher layer using a physical channel The PHY layer is connected to a medium access control (MAC) layer located on the higher layer via a transport channel. Data is transported between the MAC layer and the PHY layer via the transport channel. Data is transported between a physical layer of a transmitting side and a physical layer of a receiving side via physical channels. The physical channels use time and frequency as radio resources. In detail, the physical channel is modulated using an orthogonal frequency division multiple access (OFDMA) scheme in downlink and is modulated using a single carrier frequency division multiple access (SC-FDMA) scheme in uplink.

The MAC layer of a second layer provides a service to a radio link control (RLC) layer of a higher layer via a logical channel The RLC layer of the second layer supports reliable data transmission. A function of the RLC layer may be implemented by a functional block of the MAC layer. A packet data convergence protocol (PDCP) layer of the second layer performs a header compression function to reduce unnecessary control information for efficient transmission of an Internet protocol (IP) packet such as an IP version 4 (IPv4) packet or an IP version 6 (IPv6) packet in a radio interface having a relatively small bandwidth.

A radio resource control (RRC) layer located at the bottom of a third layer is defined only in the control plane. The RRC layer controls logical channels, transport channels, and physical channels in relation to configuration, re-configuration, and release of radio bearers (RBs). An RB refers to a service that the second layer provides for data transmission between the UE and the E-UTRAN. To this end, the RRC layer of the UE and the RRC layer of the E-UTRAN exchange RRC messages with each other.

One cell of the eNB is set to operate in one of bandwidths such as 1.25, 2.5, 5, 10, 15, and 20 MHz and provides a downlink or uplink transmission service to a plurality of UEs in the bandwidth. Different cells may be set to provide different bandwidths.

Downlink transport channels for transmission of data from the E-UTRAN to the UE include a broadcast channel (BCH) for transmission of system information, a paging channel (PCH) for transmission of paging messages, and a downlink shared channel (SCH) for transmission of user traffic or control messages. Traffic or control messages of a downlink multicast or broadcast service may be transmitted through the downlink SCH and may also be transmitted through a separate downlink multicast channel (MCH).

Uplink transport channels for transmission of data from the UE to the E-UTRAN include a random access channel (RACH) for transmission of initial control messages and an uplink SCH for transmission of user traffic or control messages. Logical channels that are defined above the transport channels and mapped to the transport channels include a broadcast control channel (BCCH), a paging control channel (PCCH), a common control channel (CCCH), a multicast control channel (MCCH), and a multicast traffic channel (MTCH).

FIG. 4 is a view showing an example of a physical channel structure used in an E-UMTS system. A physical channel includes several subframes on a time axis and several subcarriers on a frequency axis. Here, one subframe includes a plurality of symbols on the time axis. One subframe includes a plurality of resource blocks and one resource block includes a plurality of symbols and a plurality of subcarriers. In addition, each subframe may use certain subcarriers of certain symbols (e.g., a first symbol) of a subframe for a physical downlink control channel (PDCCH), that is, an L1/L2 control channel. In FIG. 4, an L1/L2 control information transmission area (PDCCH) and a data area (PDSCH) are shown. In one embodiment, a radio frame of 10 ms is used and one radio frame includes 10 subframes. In addition, one subframe includes two consecutive slots. The length of one slot may be 0.5 ms. In addition, one subframe includes a plurality of OFDM symbols and a portion (e.g., a first symbol) of the plurality of OFDM symbols may be used for transmitting the L1/L2 control information. A transmission time interval (TTI) which is a unit time for transmitting data is 1 ms.

A base station and a UE mostly transmit/receive data via a PDSCH, which is a physical channel, using a DL-SCH which is a transmission channel, except a certain control signal or certain service data. Information indicating to which UE (one or a plurality of UEs) PDSCH data is transmitted and how the UE receive and decode PDSCH data is transmitted in a state of being included in the PDCCH.

For example, in one embodiment, a certain PDCCH is CRC-masked with a radio network temporary identity (RNTI) “A” and information about data is transmitted using a radio resource “B” (e.g., a frequency location) and transmission format information “C” (e.g., a transmission block size, modulation, coding information or the like) via a certain subframe. Then, one or more UEs located in a cell monitor the PDCCH using its RNTI information. And, a specific UE with RNTI “A” reads the PDCCH and then receive the PDSCH indicated by B and C in the PDCCH information.

FIG. 5 is a diagram for a general overview of the LTE protocol architecture for the downlink.

A general overview of the LTE protocol architecture for the downlink is illustrated in FIG. 5. Furthermore, the LTE protocol structure related to uplink transmissions is similar to the downlink structure in FIG. 5, although there are differences with respect to transport format selection and multi-antenna transmission.

Data to be transmitted in the downlink enters in the form of IP packets on one of the SAE bearers (501). Prior to transmission over the radio interface, incoming IP packets are passed through multiple protocol entities, summarized below and described in more detail in the following sections:

Packet Data Convergence Protocol (PDCP, 503) performs IP header compression to reduce the number of bits necessary to transmit over the radio interface. The header-compression mechanism is based on ROHC, a standardized header-compression algorithm used in WCDMA as well as several other mobile-communication standards. PDCP (503) is also responsible for ciphering and integrity protection of the transmitted data. At the receiver side, the PDCP protocol performs the corresponding deciphering and decompression operations. There is one PDCP entity per radio bearer configured for a mobile terminal.

Radio Link Control (RLC, 505) is responsible for segmentation/concatenation, retransmission handling, and in-sequence delivery to higher layers. Unlike WCDMA, the RLC protocol is located in the eNodeB since there is only a single type of node in the LTE radio-access-network architecture. The RLC (505) offers services to the PDCP (503) in the form of radio bearers. There is one RLC entity per radio bearer configured for a terminal.

There is one RLC entity per logical channel configured for a terminal, where each RLC entity is responsible for: i) segmentation, concatenation, and reassembly of RLC SDUs; ii) RLC retransmission; and iii) in-sequence delivery and duplicate detection for the corresponding logical channel

Other noteworthy features of the RLC are: (1) the handling of varying PDU sizes; and (2) the possibility for close interaction between the hybrid-ARQ and RLC protocols. Finally, the fact that there is one RLC entity per logical channel and one hybrid-ARQ entity per component carrier implies that one RLC entity may interact with multiple hybrid-ARQ entities in the case of carrier aggregation.

The purpose of the segmentation and concatenation mechanism is to generate RLC PDUs of appropriate size from the incoming RLC SDUs. One possibility would be to define a fixed PDU size, a size that would result in a compromise. If the size were too large, it would not be possible to support the lowest data rates. Also, excessive padding would be required in some scenarios. A single small PDU size, however, would result in a high overhead from the header included with each PDU. To avoid these drawbacks, which is especially important given the very large dynamic range of data rates supported by LTE, the RLC PDU size varies dynamically.

In process of segmentation and concatenation of RLC SDUs into RLC PDUs, a header includes, among other fields, a sequence number, which is used by the reordering and retransmission mechanisms. The reassembly function at the receiver side performs the reverse operation to reassemble the SDUs from the received PDUs.

Medium Access Control (MAC, 507) handles hybrid-ARQ retransmissions and uplink and downlink scheduling. The scheduling functionality is located in the eNodeB, which has one MAC entity per cell, for both uplink and downlink. The hybrid-ARQ protocol part is present in both the transmitting and receiving end of the MAC protocol. The MAC (507) offers services to the RLC (505) in the form of logical channels (509).

Physical Layer (PHY, 511), handles coding/decoding, modulation/demodulation, multi-antenna mapping, and other typical physical layer functions. The physical layer (511) offers services to the MAC layer (507) in the form of transport channels (513).

The Logical Channel Prioritization procedure is applied when a new transmission is performed.

RRC controls the scheduling of uplink data by signalling for each logical channel: priority where an increasing priority value indicates a lower priority level, prioritisedBitRate which sets the Prioritized Bit Rate (PBR), bucketSizeDuration which sets the Bucket Size Duration (BSD).

The MAC entity shall maintain a variable Bj for each logical channel j. Bj shall be initialized to zero when the related logical channel is established, and incremented by the product PBR×TTI duration for each TTI, where PBR is Prioritized Bit Rate of logical channel j. However, the value of Bj can never exceed the bucket size and if the value of Bj is larger than the bucket size of logical channel j, it shall be set to the bucket size. The bucket size of a logical channel is equal to PBR×BSD, where PBR and BSD are configured by upper layers.

The MAC entity shall perform the following Logical Channel Prioritization procedure when a new transmission is performed. The MAC entity shall allocate resources to the logical channels in the following steps.

Step 1: All the logical channels with Bj>0 are allocated resources in a decreasing priority order. If the PBR of a logical channel is set to “infinity”, the MAC entity shall allocate resources for all the data that is available for transmission on the logical channel before meeting the PBR of the lower priority logical channels.

Step 2: the MAC entity shall decrement Bj by the total size of MAC SDUs served to logical channel j in Step 1.

Step 3: if any resources remain, all the logical channels are served in a strict decreasing priority order (regardless of the value of Bj) until either the data for that logical channel or the UL grant is exhausted, whichever comes first. Logical channels configured with equal priority should be served equally.

The UE shall also follow the rules below during the scheduling procedures above.

The UE should not segment an RLC SDU (or partially transmitted SDU or retransmitted RLC PDU) if the whole SDU (or partially transmitted SDU or retransmitted RLC PDU) fits into the remaining resources of the associated MAC entity.

If the UE segments an RLC SDU from the logical channel, it shall maximize the size of the segment to fill the grant of the associated MAC entity as much as possible.

The UE should maximize the transmission of data.

if the MAC entity is given an UL grant size that is equal to or larger than 4 bytes while having data available for transmission, the MAC entity shall not transmit only padding BSR and/or padding (unless the UL grant size is less than 7 bytes and an AMD PDU segment needs to be transmitted).

The MAC entity shall not transmit data for a logical channel corresponding to a radio bearer that is suspended.

For the Logical Channel Prioritization procedure, the MAC entity shall take into account the following relative priority in decreasing order.

MAC control element for C-RNTI or data from UL-CCCH;

MAC control element for BSR, with exception of BSR included for padding;

MAC control element for PHR, Extended PHR, or Dual Connectivity PHR;

MAC control element for Sidelink BSR, with exception of Sidelink BSR included for padding;

data from any Logical Channel, except data from UL-CCCH;

MAC control element for BSR included for padding;

MAC control element for Sidelink BSR included for padding.

When the MAC entity is requested to transmit multiple MAC PDUs in one TTI, steps 1 to 3 and the associated rules may be applied either to each grant independently or to the sum of the capacities of the grants. Also the order in which the grants are processed is left up to UE implementation. It is up to the UE implementation to decide in which MAC PDU a MAC control element is included when MAC entity is requested to transmit multiple MAC PDUs in one TTI. When the UE is requested to generate MAC PDU(s) in two MAC entities in one TTI, it is up to UE implementation in which order the grants are processed.

FIG. 6 is an example of default data path for communication between two UEs. With reference to FIG. 6, even when two UEs (e.g., UE1, UE2) in close proximity communicate with each other, their data path (user plane) goes via the operator network. Thus a typical data path for the communication involves eNB(s) and/or Gateway(s) (GW(s)) (e.g., SGW/PGW).

FIGS. 7 and 8 are examples of data path scenarios for a proximity communication. If wireless devices (e.g., UE1, UE2) are in proximity of each other, they may be able to use a direct mode data path (FIG. 7) or a locally routed data path (FIG. 8). In the direct mode data path, wireless devices are connected directly each other (after appropriate procedure(s), such as authentication), without eNB and SGW/PGW. In the locally routed data path, wireless devices are connected each other through eNB only.

FIG. 9 is a conceptual diagram illustrating for a non-roaming reference architecture.

PC1 to PC5 represent interfaces. PC1 is a reference point between a ProSe application in a UE and a ProSe App server. It is used to define application level signaling requirements. PC2 is a reference point between the ProSe App Server and the ProSe Function. It is used to define the interaction between ProSe App Server and ProSe functionality provided by the 3GPP EPS via ProSe Function. One example may be for application data updates for a ProSe database in the ProSe Function. Another example may be data for use by ProSe App Server in interworking between 3GPP functionality and application data, e.g. name translation. PC3 is a reference point between the UE and ProSe Function. It is used to define the interaction between UE and ProSe Function. An example may be to use for configuration for ProSe discovery and communication. PC4 is a reference point between the EPC and ProSe Function. It is used to define the interaction between EPC and ProSe Function. Possible use cases may be when setting up a one-to-one communication path between UEs or when validating ProSe services (authorization) for session management or mobility management in real time.

PC5 is a reference point between UE to UE used for control and user plane for discovery and communication, for relay and one-to-one communication (between UEs directly and between UEs over LTE-Uu). Lastly, PC6 is a reference point may be used for functions such as ProSe Discovery between users subscribed to different PLMNs.

EPC (Evolved Packet Core) includes entities such as MME, S-GW, P-GW, PCRF, HSS etc. The EPC here represents the E-UTRAN Core Network architecture. Interfaces inside the EPC may also be impacted albeit they are not explicitly shown in FIG. 9.

Application servers, which are users of the ProSe capability for building the application functionality, e.g. in the Public Safety cases they can be specific agencies (PSAP) or in the commercial cases social media. These applications are defined outside the 3GPP architecture but there may be reference points towards 3GPP entities. The Application server can communicate towards an application in the UE.

Applications in the UE use the ProSe capability for building the application functionality. Example may be for communication between members of Public Safety groups or for social media application that requests to find buddies in proximity The ProSe Function in the network (as part of EPS) defined by 3GPP has a reference point towards the ProSe App Server, towards the EPC and the UE.

The functionality may include but not restricted to e.g.:

Interworking via a reference point towards the 3rd party Applications

Authorization and configuration of the UE for discovery and Direct communication

Enable the functionality of the EPC level ProSe discovery

ProSe related new subscriber data and/handling of data storage; also handling of ProSe identities;

Security related functionality

Provide Control towards the EPC for policy related functionality

Provide functionality for charging (via or outside of EPC, e.g. offline charging)

Especially, the following identities are used for ProSe Direct Communication:

Source Layer-2 ID identifies a sender of a D2D packet at PC5 interface. The Source Layer-2 ID is used for identification of the receiver RLC UM entity;

Destination Layer-2 ID identifies a target of the D2D packet at PC5 interface. The Destination Layer-2 ID is used for filtering of packets at the MAC layer. The Destination Layer-2 ID may be a broadcast, groupcast or unicast identifier; and

SA L1 ID identifier in Scheduling Assignment (SA) at PC5 interface. SA L1 ID is used for filtering of packets at the physical layer. The SA L1 ID may be a broadcast, groupcast or unicast identifier.

No Access Stratum signaling is required for group formation and to configure Source Layer-2 ID and Destination Layer-2 ID in the UE. This information is provided by higher layers.

In case of groupcast and unicast, the MAC layer will convert the higher layer ProSe ID (i.e. ProSe Layer-2 Group ID and ProSe UE ID) identifying the target (Group, UE) into two bit strings of which one can be forwarded to the physical layer and used as SA L1 ID whereas the other is used as Destination Layer-2 ID. For broadcast, L2 indicates to L1 that it is a broadcast transmission using a pre-defined SA L1 ID in the same format as for group- and unicast.

FIG. 10 is a conceptual diagram illustrating for a Layer 2 structure for Sidelink. The Sidelink is UE to UE interface for ProSe direct communication and ProSe Direct Discovery. Correspond to the PC5 interface. The Sidelink comprises ProSe Direct Discovery and ProSe Direct Communication between UEs. The Sidelink uses uplink resources and physical channel structure similar to uplink transmissions. However, some changes, noted below, are made to the physical channels. E-UTRA defines two MAC entities; one in the UE and one in the E-UTRAN. These MAC entities handle the following transport channels additionally, i) sidelink broadcast channel (SL-BCH), ii) sidelink discovery channel (SL-DCH) and iii) sidelink shared channel (SL-SCH).

Basic transmission scheme: the Sidelink transmission uses the same basic transmission scheme as the UL transmission scheme. However, sidelink is limited to single cluster transmissions for all the sidelink physical channels. Further, sidelink uses a 1 symbol gap at the end of each sidelink sub-frame.

Physical-layer processing: the Sidelink physical layer processing of transport channels differs from UL transmission in the following steps:

i) Scrambling: for PSDCH and PSCCH, the scrambling is not UE-specific;

ii) Modulation: 64 QAM is not supported for Sidelink.

Physical Sidelink control channel: PSCCH is mapped to the Sidelink control resources. PSCCH indicates resource and other transmission parameters used by a UE for PSSCH.

Sidelink reference signals: for PSDCH, PSCCH and PSSCH demodulation, reference signals similar to uplink demodulation reference signals are transmitted in the 4th symbol of the slot in normal CP and in the 3rd symbol of the slot in extended cyclic prefix. The Sidelink demodulation reference signals sequence length equals the size (number of sub-carriers) of the assigned resource. For PSDCH and PSCCH, reference signals are created based on a fixed base sequence, cyclic shift and orthogonal cover code.

Physical channel procedure: for in-coverage operation, the power spectral density of the sidelink transmissions can be influenced by the eNB.

FIG. 11a is a conceptual diagram illustrating for User-Plane protocol stack for ProSe Direct Communication, and FIG. 11b is Control-Plane protocol stack for ProSe Direct Communication.

FIG. 11a shows the protocol stack for the user plane, where PDCP, RLC and MAC sublayers (terminate at the other UE) perform the functions listed for the user plane (e.g. header compression, HARQ retransmissions). The PC5 interface consists of PDCP, RLC, MAC and PHY as shown in FIG. 11 a.

User plane details of ProSe Direct Communication: i) MAC sub header contains LCIDs (to differentiate multiple logical channels), ii) The MAC header comprises a Source Layer-2 ID and a Destination Layer-2 ID, iii) At MAC Multiplexing/demultiplexing, priority handling and padding are useful for ProSe Direct communication, iv) RLC UM is used for ProSe Direct communication, v) Segmentation and reassembly of RLC SDUs are performed, vi) A receiving UE needs to maintain at least one RLC UM entity per transmitting peer UE, vii) An RLC UM receiver entity does not need to be configured prior to reception of the first RLC UM data unit, and viii) U-Mode is used for header compression in PDCP for ProSe Direct Communication.

FIG. 11b shows the protocol stack for the control plane, where RRC, RLC, MAC, and PHY sublayers (terminate at the other UE) perform the functions listed for the control plane. A D2D UE does not establish and maintain a logical connection to receiving D2D UEs prior to a D2D communication.

FIG. 12 is a conceptual diagram illustrating for a PC5 interface for ProSe Direct Discovery.

ProSe Direct Discovery is defined as the procedure used by the ProSe-enabled UE to discover other ProSe-enabled UE(s) in its proximity using E-UTRA direct radio signals via PC5.

Radio Protocol Stack (AS) for ProSe Direct Discovery is shown in FIG. 12.

The AS layer performs the following functions:

Interfaces with upper layer (ProSe Protocol): The MAC layer receives the discovery information from the upper layer (ProSe Protocol). The IP layer is not used for transmitting the discovery information.

Scheduling: The MAC layer determines the radio resource to be used for announcing the discovery information received from upper layer.

Discovery PDU generation: The MAC layer builds the MAC PDU carrying the discovery information and sends the MAC PDU to the physical layer for transmission in the determined radio resource. No MAC header is added.

There are two types of resource allocation for discovery information announcement.

Type 1: A resource allocation procedure where resources for announcing of discovery information are allocated on a non UE specific basis, further characterized by: i) The eNB provides the UE(s) with the resource pool configuration used for announcing of discovery information. The configuration may be signalled in SIB, ii) The UE autonomously selects radio resource(s) from the indicated resource pool and announce discovery information, iii) The UE can announce discovery information on a randomly selected discovery resource during each discovery period.

Type 2: A resource allocation procedure where resources for announcing of discovery information are allocated on a per UE specific basis, further characterized by: i) The UE in RRC_CONNECTED may request resource(s) for announcing of discovery information from the eNB via RRC, ii) The eNB assigns resource(s) via RRC, iii) The resources are allocated within the resource pool that is configured in UEs for monitoring.

For UEs in RRC_IDLE, the eNB may select one of the following options:

The eNB may provide a Type 1 resource pool for discovery information announcement in SIB. UEs that are authorized for Prose Direct Discovery use these resources for announcing discovery information in RRC_IDLE.

The eNB may indicate in SIB that it supports D2D but does not provide resources for discovery information announcement. UEs need to enter RRC Connected in order to request D2D resources for discovery information announcement.

For UEs in RRC_CONNECTED,

A UE authorized to perform ProSe Direct Discovery announcement indicates to the eNB that it wants to perform D2D discovery announcement.

The eNB validates whether the UE is authorized for ProSe Direct Discovery announcement using the UE context received from MME.

The eNB may configure the UE to use a Type 1 resource pool or dedicated Type 2 resources for discovery information announcement via dedicated RRC signaling (or no resource).

The resources allocated by the eNB are valid until a) the eNB de-configures the resource(s) by RRC signaling or b) the UE enters IDLE. (FFS whether resources may remain valid even in IDLE).

Receiving UEs in RRC_IDLE and RRC_CONNECTED monitor both Type 1 and Type 2 discovery resource pools as authorized. The eNB provides the resource pool configuration used for discovery information monitoring in SIB. The SIB may contain discovery resources used for announcing in neighbor cells as well.

Recently, the extension of network coverage using L3-based UE-to-Network Relay is expected to be supported. When the UE starts ProSe communication within the network and then moves out of the coverage, the relay may be selected by the UE or the network for service coverage extension. During changing the traffic path of the (potential) remote UE from eNB to a relay, there could be service interruption if the relaying service activation (including relay selection) for the remote UE is performed too late. On the contrary, if the relaying service activation is performed early, the remote UE might have dual connectivity for the same (or different) PDN connection(s) where one connectivity goes through the eNB and another goes through relay. In addition, the (potential) UE may establish unnecessary connection between relay.

The serving cell of a relay and a remote UE might be different. Depending on whether the network supports the resource coordination between the serving cell of the relay and the serving of the remote UE, it would be beneficial to limit the relay selection to the relay belonging to the same cell of the cell of the remote UE.

FIG. 13 is an exemplary diagram for explaining the D2D environment. Referring to FIG. 13, discovery and communication between relay UE and the remote UE is possible even in a scenario where two UEs are staying in different cells. However, under the scenario of cell for ProSe of L2 relay is different from cell for ProSe of the remote UE is different, it may not be possible to perform direct discovery and direct communication since the L2 configuration and resource are configured by Cell 2 while remote UE transmits the message with the synchronization of Cell 1.

To solve the problem, it is proposed of method of selecting the synchronization reference for transmitting discovery/communication message by the remote UE. This invention may be applied to the remote UE which are staying in (camping on/connected to) another/same cell from the cell of the connected relay UE. Specific details will be described below.

In the present invention, the following may be assumed.

The sidelink procedure is operated in serving carrier of the remote UE or in dedicated carrier for sidelink operation. The technology for sidelink operation involves LTE sidelink and UE to network relaying over non-3GPP access (e.g. using WiFi/Bluetooth).

The relay UE may be UE to UE relay as well as UE to network relay.

The sidelink may refer to the link between relay UE and remote UE.

The remote UE may be currently connected to the network via relay UE.

The example measurement result of sidelink may be SD-RSRP/RSRQ, RSSI, SINR and/or RSRP/Q. Other measurement result can be also used. In case of relaying over non-3GPP RAT, the measurement could be performed for the beacon or data part.

The remote UE may transmit to/receive from the same cell.

Network Assisted Autonomous Selection Method

FIG. 14 is a flow chart according to an embodiment of the present invention.

Referring to FIG. 14, the remote UE may receive a message for a sidelink resource configuration (S1410). Specifically, since the remote UE in a coverage of cell 1 is connected to the cell 2 through the relay UE in a coverage of cell 2, the remote UE may receive the message from the cell 2 via the relay UE. For this, it may be assumed that if remote UE is linked/connected to relay UE, the cell 2 is able to know existence of the connected remote UE and configure the remote UE (e.g. L1/2 configuration, sidelink resource configuration). In this case, the cell 2 which provides configuration used for sidelink communication/discovery is regarded as serving cell to the remote UE. Serving cell of the remote UE is same as that of the connected relay UE.

In addition, the remote UE may be provided with predetermined threshold (e.g. RSRP/RSRQ threshold) for determining which cell to be used for synchronization reference cell for transmitting ProSe messages (e.g. discovery/communication message) via broadcast/dedicated signalling from cell 2.

Subsequently, the remote UE may select a synchronization reference cell (S1420). Specifically, the remote UE may select a synchronization reference cell using a predetermined threshold. For this, the remote UE may measure a channel quality of the cell 2 or one or more neighboring cells of the remote UE.

For example, if channel quality of the cell 2 of the remote UE is less than the provided predetermined threshold (e.g. RSRP/RSRQ or RSRP/RSRQ−hysteresis value (if configured)), the remote UE may select other cell as synchronization reference cell. As an example, the cell 1 may be the synchronization reference cell. As another example, the other cell may be best ranked cell on the frequency of channel quality is being measured for the above comparison. Otherwise, if channel quality of the cell 2 is higher than or equal to the predetermined threshold (e.g. RSRP/RSRQ or RSRP/RSRQ+hysteresis value (if configured)), the remote UE may select the cell 2 as synchronization reference cell.

After selecting the synchronization reference cell, the remote UE may perform synchronization to the indicated cell when transmitting sidelink communication, sidelink discovery or synchronization information.

Subsequently, the remote UE may transmit a sidelink data to the relay UE. Specifically, the remote UE may transmit the sidelink data to the second UE using the sidelink resource configuration received from the cell 2 based on the synchronization acquired from a synchronization signal of the cell 1.

According to an embodiment of the present invention, the interference problem caused by transmitting, by the remote UE in the coverage of the cell 1, a signal based on the synchronization of cell 2 can be solved in the coverage of the cell 1.

Network Based Selection Method

According to another aspect, the remote UE may receive the instruction of the network and select the synchronous reference signal based on the received instruction.

The remote UE may report information of the channel quality (e.g. RSRP/RSRQ measurement) to the network. Based on the reported information of the remote UE, the network may determine the synchronization reference cell for the remote UE and indicates the selected synchronization reference cell identity.

For example, the cell 2 may provide RSRP/RSRQ threshold for reporting the measurement results of serving cell and/or neighbor cells to the remote UE. If the channel quality of the cell 2 is less than or equal to the provided threshold (e.g. event A2), the remote UE may report the channel quality of cell 2 and available channel quality of best neighboring cell on the same frequency and the associated cell identity to the network. If the channel quality of the cell 2 is higher than the provided threshold (e.g. event A1), the remote UE may report the available channel quality of cell 2 and/or neighbor cells and the associated cell identity.

Subsequently, the network may indicate the cell identity of reported best ranked neighbor cell in the same frequency of the current cell to be used for the synchronization reference cell of the remote UE. If the cell 1 is selected as synchronization reference cell of the remote UE, the network provides cell 1 as synchronization reference cell of the remote UE. If the cell 2 is selected as synchronization reference cell of the remote UE, the network might omit the signaling. If there is no synchronization reference cell via dedicated signalling, the remote UE consider the current cell as synchronization reference cell for transmitting communication/discovery message.

Subsequently, the UE may perform synchronization to the indicated cell when transmitting sidelink communication, sidelink discovery or synchronisation information.

FIG. 15 is a flowchart for explaining an embodiment of the present invention.

In this example, it is assumed that best ranked cell of the remote UE is Cell1 and at first remote UE is connected to Cell1. Referring to FIG. 15, the relay UE may be connected to/served by Cell2. Measurement for sidelink relay is triggered by comparing serving cell RSRP/RSRQ with RSRP/RSRQ threshold as in Rel-13 relay discovery in remote UE. It may be also assumed that the serving cell measurement and intra-frequency neighbor cell measurement is currently being performed.

When the remote UE finds the candidate relay UE(s), the remote UE may inform the found candidate relay UE(s) to the currently connected cell (i.e. Cell1) with the assistance information (e.g. found relay UE ID, link quality between remote UE and found relay UE(s), cell identity of relay UE(s) and remote UE ID). Remote UE ID may refer to the existing ProSe UE ID or new identity.

Subsequently, Cell2 may be provided with UE context information from Cell1 since Cell2 is required to make a decision on UE configuration as in legacy handover. After receiving UE context information, Cell2 provides configuration of remote UE, sidelink configuration (e.g. resource configuration, sync configuration) to Cell1. The sync information includes RSRP/RSRQ threshold and optionally hysteresis value. Then, Cell1 forwards the received configuration to the remote UE.

After receiving the configuration from Cell2, the remote UE considers itself being connected to the Cell2. From the relay UE point of view, in order not to filter out the message from remote UE, the network may provide the remote UE identity (L2 identity, e.g. ProSe UE ID). The remote UE filter out other sidelink communication messages from the remote UE which the relay UE does not know.

If RSRP of Cell2 is lower than or equal to given threshold, the remote UE selects best ranked intra-frequency neighbour cell (i.e. Cell1 in this example) as synchronization reference cell. Otherwise, the remote UE selects Ce112 as synchronization reference cell.

FIG. 16 is a block diagram of a communication apparatus according to an embodiment of the present invention.

The apparatus shown in FIG. 16 can be a user equipment (UE) and/or eNB adapted to perform the above mechanism, but it can be any apparatus for performing the same operation.

As shown in FIG. 16, the apparatus may comprise a DSP/microprocessor (110) and RF module (transceiver; 135). The DSP/microprocessor (110) is electrically connected with the transceiver (135) and controls it. The apparatus may further include power management module (105), battery (155), display (115), keypad (120), SIM card (125), memory device (130), speaker (145) and input device (150), based on its implementation and designer's choice.

Specifically, FIG. 16 may represent a UE comprising a receiver (135) configured to receive a request message from a network, and a transmitter (135) configured to transmit the transmission or reception timing information to the network. These receiver and the transmitter can constitute the transceiver (135). The UE further comprises a processor (110) connected to the transceiver (135: receiver and transmitter).

Also, FIG. 16 may represent a network apparatus comprising a transmitter (135) configured to transmit a request message to a UE and a receiver (135) configured to receive the transmission or reception timing information from the UE. These transmitter and receiver may constitute the transceiver (135). The network further comprises a processor (110) connected to the transmitter and the receiver. The processor (110) is configured to perform operations according to the embodiment of the present invention exemplarily described with reference to the accompanying drawings. In particular, the detailed operations of the processor (110) can refer to the contents described with reference to FIGS. 1 to 15.

The embodiments of the present invention described herein below are combinations of elements and features of the present invention. The elements or features may be considered selective unless otherwise mentioned. Each element or feature may be practiced without being combined with other elements or features. Further, an embodiment of the present invention may be constructed by combining parts of the elements and/or features. Operation orders described in embodiments of the present invention may be rearranged. Some constructions of any one embodiment may be included in another embodiment and may be replaced with corresponding constructions of another embodiment. It is obvious to those skilled in the art that claims that are not explicitly cited in each other in the appended claims may be presented in combination as an embodiment of the present invention or included as a new claim by subsequent amendment after the application is filed.

In the embodiments of the present invention, a specific operation described as performed by the BS may be performed by an upper node of the BS. Namely, it is apparent that, in a network comprised of a plurality of network nodes including a BS, various operations performed for communication with an MS may be performed by the BS, or network nodes other than the BS. The term ‘eNB’ may be replaced with the term ‘fixed station’, ‘Node B’, ‘Base Station (BS)’, ‘access point’, etc.

The above-described embodiments may be implemented by various means, for example, by hardware, firmware, software, or a combination thereof.

In a hardware configuration, the method according to the embodiments of the present invention may be implemented by one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers, microcontrollers, or microprocessors.

In a firmware or software configuration, the method according to the embodiments of the present invention may be implemented in the form of modules, procedures, functions, etc. performing the above-described functions or operations. Software code may be stored in a memory unit and executed by a processor. The memory unit may be located at the interior or exterior of the processor and may transmit and receive data to and from the processor via various known means.

Those skilled in the art will appreciate that the present invention may be carried out in other specific ways than those set forth herein without departing from essential characteristics of the present invention. The above embodiments are therefore to be construed in all aspects as illustrative and not restrictive. The scope of the invention should be determined by the appended claims, not by the above description, and all changes coming within the meaning of the appended claims are intended to be embraced therein. 

What is claimed is:
 1. A method for acquiring, by a first user equipment (UE) in a coverage of a first cell, synchronization in a wireless communication system, the method comprising: receiving a message for a sidelink resource configuration from a second cell through the second UE in a coverage of the second cell; if a channel quality of the second cell is less than a predetermined threshold, selecting the first cell as a synchronization reference cell; and transmitting a sidelink data to the second UE using the sidelink resource configuration based on the synchronization acquired from a synchronization signal of the first cell.
 2. The method of claim 1, wherein if the channel quality of the second cell is higher than or equal to the predetermined threshold, the second cell is selected as the synchronization reference cell.
 3. The method of claim 1, wherein the method further comprising measuring a channel quality of the second cell and one or more neighboring cells of the first UE.
 4. The method of claim 3, wherein if the channel quality of the second cell is less than the predetermined threshold, the first UE selects one of the one or more neighboring cells as the synchronization reference cell based on the channel quality.
 5. The method of claim 1, wherein the method further comprising acquiring the synchronization from the synchronization signal of the first cell.
 6. The method of claim 1, wherein the predetermined threshold is received from the second cell.
 7. The method of claim 1, wherein the first UE is connected to the second cell through the second UE.
 8. A first user equipment (UE) in a coverage of a first cell in a wireless communication system, the first UE comprising: a transceiver; and a processor connected with the transceiver, wherein the processor is configured to: control the transceiver to receive a message for a sidelink resource configuration from a second cell through the second UE in a coverage of the second cell, if a channel quality of the second cell is less than a predetermined threshold, select the first cell as a synchronization reference cell, and control the transceiver to transmit a sidelink data to the second UE using the sidelink resource configuration based on the synchronization acquired from a synchronization signal of the first cell.
 9. The UE of claim 8, wherein if the channel quality of the second cell is higher than or equal to the predetermined threshold, the second cell is selected as the synchronization reference cell.
 10. The UE of claim 8, wherein the processor is further configured to measure a channel quality of the second cell and one or more neighboring cells of the first UE.
 11. The UE of claim 10, wherein if the channel quality of the second cell is less than the predetermined threshold, the first UE selects one of the one or more neighboring cells as the synchronization reference cell based on the channel quality.
 12. The UE of claim 8, wherein the processor is further configured to acquire the synchronization from the synchronization signal of the first cell.
 13. The UE of claim 8, wherein the predetermined threshold is received from the second cell.
 14. The UE of claim 8, wherein the first UE is connected to the second cell through the second UE. 